responseStr = 'fetchJSON_comment98({"jwotestProduct":null,"score":0,"comments":[{"id":15367856622}]});'

import re
res = re.match("(fetchJSON_comment98\()(.*)(\);)",responseStr)
# print(res.group(0))
# print(res.group(1))
# print(res.group(2))
# print(res.group(3))
import json
jsonObj = json.loads(res.group(2))
print(jsonObj['comments'])